[llvm] [VPlan] Delay adding canonical IV increment. (PR #82270)

[via llvm-commits]

================
@@ -1454,52 +1454,30 @@ void VPlanTransforms::optimize(VPlan &Plan) {
   licm(Plan);
 }
 
-// Add a VPActiveLaneMaskPHIRecipe and related recipes to \p Plan and replace
-// the loop terminator with a branch-on-cond recipe with the negated
-// active-lane-mask as operand. Note that this turns the loop into an
-// uncountable one. Only the existing terminator is replaced, all other existing
-// recipes/users remain unchanged, except for poison-generating flags being
-// dropped from the canonical IV increment. Return the created
+// Add a VPActiveLaneMaskPHIRecipe and recipes to compute its start lane mask to
+// \p Plan, but w/o its increment in the loop region or adjusting the exit
+// conditions of the loop region - those are adjusted later. Return the created
----------------
ayalz wrote:

This essentially introduces VPActiveLaneMaskPHIRecipe as a placeholder.

https://github.com/llvm/llvm-project/pull/82270